Image formation for silver halide photographs is, in general, carried out utilizing the reducing effect of developing agent such as hydroquinone, or the like contained in a developing solution. In this process, the activity of a developing agent increases, and the rate of development increases, with a decrease in the concentration of hydrogen ions in the developing solution, that is, with an increase in the pH of the solution. Thus, a conventional developing solution contains a dissolved alkali agent, such as sodium hydroxide, to provide a high pH value. However, a solution of high pH is difficult to handle and must be handled carefully, and a developing agent in such a developing solution of high pH value is easily oxidized by oxygen in the air, so that such a developing solution has disadvantages.
To overcome these problems, a method using a combination of sodium oxalate and zinc hydroxide has been disclosed in U.S. Pat. No. 3,260,598. According to this method, one of these two compounds is added to a silver halide light-sensitive material, the other is added to a treating solution. By developing the light-sensitive material, the two compounds react with each other, so as to release an alkali and to increase the pH value.
However, this method provides an image having deteriorated graininess.
To improve graininess, the grain size of the silver halide emulsion is reduced, but this is not useful, because it lowers the sensitivity of the light-sensitive material. Other methods are proposed which use hardening agents such as formaldehyde and the like, for example, the compounds mentioned in U.S. Pat. Nos. 2,080,019, 2,725,294, 2,725,295, 2,725,305, 2,726,162, 2,732,316, 2,870,013, 2,950,197, and 3,103,437, and Canadian Pat. No. 588,451. However, those methods do not have sufficiently improved graininess.
Further, it has been proposed to increase the iodine content in silver halide emulsion grains in a silver halide black-and-white negative photographic material, but this method has not sufficiently improved graininess.